Weilong Quan

Structural, mechanical and tribological characterizations of a-C: H: Si films prepared by a hybrid PECVD and sputtering technique

a-C : H : Si films were prepared under different CH4/Ar ratios by a hybrid radio frequency plasma-enhanced chemical vapour deposition (RFPECVD) and unbalanced magnetron sputtering technique. Characterizations showed that the CH4/Ar ratio affected not only the content but also the chemical state of the doped Si, thus further affecting the microstructures, mechanical and tribological performances of the a-C : H : Si films. Generally, when the CH4/Ar ratio was low (≤4/2), the Si-doping content dropped with increased CH4 percentage, accompanied by a decreased sp3(C–Si+C–C)/sp2(C=C), increased ID/IG ratio and up-shift of the G peak position, as can be seen from the Raman spectra, while at a higher CH4 percentage (e.g. CH4/Ar = 5/2), the prepared a-C : H : Si films exhibited a series of aberrant properties due to the incorporation of abundant H and the high oxidization of the doped Si. Another unique characteristic of our films was the presence of numerous Si–Si bonds at high Si content, which was not observed in the a-C : H : Si films produced by the decomposition of Si-containing gaseous precursors. Moreover, although Si incorporation improved such properties of the DLC films as adhesion strength, internal stress and tribological moisture sensitivity, its effectiveness in enhancing the mechanical and tribological performances were governed not by the Si-doping content or sp3-C fraction but by the film continuity or adhesion (minimized interlinking destruction by the Si–H, C–H, Si–O–Si bonds) and sp2(C=C) fraction (based on the film continuity).

The effect of duty cycle on the microstructure and properties of graphite-like amorphous carbon films prepared by unbalanced magnetron sputtering

The effect of duty cycle on the microstructure and properties of graphite-like amorphous carbon films prepared by unbalanced magnetron sputtering was investigated. The structure of the resultant carbon film is amorphous, as shown by high-resolution transmission electron microscopy. Raman analysis shows that the studied films are dominated by sp2 sites, and the intensity ratio of the D and G peaks ranges from 4.0 at a duty cycle of 20% to 6.0 at 50%, which is one order of magnitude larger than that of diamond-like carbon films, indicating an obvious increase in sp2 sites with duty cycle. The surface morphology was investigated by atomic force microscopy. The images show that the as-deposited carbon films have a very rough surface, and the maximum granular structure size is up to 180 nm in diameter and 50 nm in height. The hardness and internal stress of the resultant carbon films increase with increasing duty cycle, accompanied by an increase in sp2 fraction in the films, which is different from the diamond-like carbon films. In addition, the resultant carbon films show superior tribological properties with high load-bearing capacity and excellent wear resistance. The influence of duty cycle on the microstructure and properties is discussed in detail.

Fullerene-like hydrogenated carbon films with super-low friction and wear, and low sensitivity to environment

A novel hydrogenated carbon film containing fullerene-like nanostructure was prepared by pulse bias-assisted plasma enhanced chemical vapour deposition, and the fullerene-like arrangement in the film was characterized by high resolution transmission electron microscopy. The as-prepared hydrogenated carbon film exhibited super-low friction and wear in both dry N2 and humid ambient atmospheres, and was superior to the conventional hydrogenated carbon films. These excellent tribological properties could be attributed to the unique fullerene-like nanostructure, which endows the film with some special chemical and physical features, such as high chemical inertness, hardness and elastic recovery owing to the closed, curved and caged graphite planes, and hence, improves the tribological properties of the hydrogenated carbon film.

Effects of pulse bias duty cycle on fullerenelike nanostructure and mechanical properties of hydrogenated carbon films prepared by plasma enhanced chemical vapor deposition method

Fullerenelike hydrogenated carbon films were produced by pulse bias-assisted rf inductively coupled plasma enhanced chemical vapor deposition (ICPECVD). The effects of pulse duty cycle on the microstructure and mechanical properties of the resultant films were investigated by means of high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, nanoindentation, and stress measurement. The low pulse duty cycle was found the key in the formation of fullerenelike structure in hydrogenated carbon films, and thus increased the hardness, elasticity, and internal stress of the films. The role of pulse duty cycle in evolution of fullerenelike structure was also discussed in terms of ion bombardment, hydrogen removal, and “annealing” effects.

Effects of environmental molecular characteristics and gas–surface interaction on friction behaviour of diamond-like carbon films

The superlow friction behaviours of diamond-like carbon (DLC) films in three different inert environments (dry N2, CO2 and Ar gas) were investigated and compared. The friction of the DLC films in dry N2 and CO2 was superior to that in dry Ar, and was dependent on the environmental exposure time. The possible reason is that N2 and CO2 have the same molecular characteristic of lone pair electrons at both sides of the molecules, while Ar has no lone pair electrons. And a special gas–surface interaction due to π orbital–lone pair electrons interactions is present at the sliding interfaces of DLC films in dry CO2 and N2. A friction model in relation to environmental molecular characteristics and gas–surface interactions was proposed to explain the friction behaviours of DLC films.